Fix value of CMake variable ARCANE_MSBUILD_EXEC in ArcaneSwigConfig.cmake.in

[grospelliergilles]

This variable used the dotnet wrapper added in #1791, but it should use the real path of the executable because the wrapper is not installed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.24%. Comparing base (304b757) to head (7ad3e3b).
Report is 7 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1830      +/-   ##
==========================================
- Coverage   70.24%   70.24%   -0.01%     
==========================================
  Files        2263     2263              
  Lines      162812   162812              
  Branches    18767    18766       -1     
==========================================
- Hits       114363   114362       -1     
- Misses      41669    41672       +3     
+ Partials     6780     6778       -2     

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